In most RFID systems, an interrogator, such as an RFID reader, searches all RFID tags within an effective range to perform further operations. FIG. 1 is a flow chart of a conventional method of an interrogator searching RFID tags. The flow begins with Step 10. In Step 12, a protocol applied to the method is defined. In Step 14, it is determined whether there are a plurality of RFID tags be searched simultaneously. In Step 16, when the answer is no, for example, when there is only one RFID tag to be searched, a UID of the RFID tag is directly stored. In Step 18, when there are multiple RFID tags to be searched simultaneously, a search mechanism is implemented for searching. In Step 20, after the respective UIDs of the plurality of RFID tags are identified, the UIDs of the plurality of RFID tags are respectively stored. The flow ends with Step 22. Most RFID technologies apply the foregoing method for searching. However, a certain method is only applicable to one protocol such that the method offers little user flexibility. Therefore, there exists a need to design a search method applicable to various protocols and apparatus thereof, thereby improving search efficiency.